1. Field of the Invention
The present invention relates to an EL display (electronic device) formed by fabricating an EL (electro luminescence) element on a substrate. Particularly, the present invention relates to an EL display using a semiconductor element (an element employing a semiconductor thin film), and furthermore to electronic equipment using the EL display as a display portion.
2. Description of the Related Art
In recent years, remarkable progress has been made in a technique for forming TFTs on a substrate, and developing the application of TFTs to an active matrix display device is proceeding. TFTs using a poly-silicon film, in particular, have a higher electric field effect mobility (also referred to as mobility) than that of conventional TFTs using an amorphous silicon film, and hence a high speed operation may be made. Thus, control of pixels, which in the past has been controlled by a driver circuit external to a substrate, can now be made by driver circuits formed on the same substrate as the pixels.
Various merits such as reduction of manufacturing cost, miniaturization of a display device, and increase of yield and reduction of throughput can be obtained from such an active matrix display device by forming various circuits and elements on the same substrate.
A research on active matrix EL displays having an EL element as a self-luminous element is being actively carried out. The EL display is also referred to as an organic EL display (OLED) or an organic light emitting diode (OLED).
Unlike a liquid crystal display, the EL display is a self-luminous type. The EL element has a structure composed of a pair of electrodes (anode and cathode) and an EL layer, which is usually a laminate structure, sandwiched therebetween. The laminate structure (hole transporting layer, light-emitting layer, electron transporting layer) proposed by Tang, et al. from Eastman Kodak Company can be cited as a typical laminate structure of the EL layer. This laminate structure has an extremely high luminescence efficiency, and therefore at present, most of the EL displays in which research and development are proceeding adopt this laminate structure of the EL layer.
In addition to the above laminate structure, a structure in which the layers are laminated on the anode in the order of a hole injection layer, a hole transporting layer, a light-emitting layer, and an electron transporting layer or in the order of a hole injection layer, a hole transporting layer, a light-emitting layer, an electron transporting layer, and an electron injection layer may be formed. The light-emitting layer may be doped with a fluorescent pigment or the like.
The EL layer is a generic term in the present specification indicating all the layers formed between the cathode and anode. Therefore, the above-mentioned hole injection layer, the hole transporting layer, the light-emitting layer, the electron transporting layer, the electron injection layer, etc. are all included in the EL layer.
A predetermined voltage from the pair of electrodes is applied to the EL layer having the above structure, whereby a re-coupling of carriers in the light-emitting layer occurs to thereby emit light. It is to be noted that throughout the present specification, the emission of light by the EL element is called driving the EL element. In addition, a luminescent element formed of the anode, the EL layer, and the cathode is called the EL element in the present specification.
A driving method of the analog system (analog drive) can be cited as a driving method of the EL display. An explanation regarding the analog drive of the EL display will be made with references to FIGS. 18 and 19.
FIG. 18 is a diagram showing the structure of a pixel portion in the EL display having the analog drive. A gate signal line (plurality of gate signal lines G1 to Gy) for inputting a gate signal from a gate signal line driver circuit is connected to a gate electrode of a switching TFT 1801 of the respective pixels. As to a source region and a drain region of the switching TFT 1801 of the respective pixels, one is connected to a source signal line (also called data signal line) (S1 to Sx) for inputting an analog video signal whereas the other is connected to a gate electrode of an EL driver TFT 1804 and a capacitor 1808 of each of the pixels, respectively.
A source region of the EL driver TFT 1804 of each of the pixels is connected to power supply lines (V1 to Vx), and a drain region thereof is connected to an EL element 1806, respectively. An electric potential of the power supply lines (V1 to Vx) is called a power supply potential. Each of the power supply lines (V1 to Vx) is connected to the capacitor 1808 of the respective pixels.
The EL element 1806 is composed of an anode, a cathode, and an EL layer sandwiched therebetween. When the anode of the EL element 1806 is connected to either the source region or the drain region of the EL driver TFT 1804, the anode and the cathode of the EL element 1806 become a pixel electrode and an opposing electrode, respectively. Alternatively, if the cathode of the EL element 1806 is connected to either the source region or the drain region of the EL driver TFT 1804, then the anode of the EL element 1806 becomes the opposing electrode whereas the cathode thereof becomes the pixel electrode.
It is to be noted that in the present specification, an electric potential of the opposing electrode is referred to as an opposing electric potential. An EL driver voltage, which is the electric potential difference between an electric potential of the pixel electrode and an electric potential of the opposing electrode, is applied to the EL layer.
FIG. 19 is a timing chart illustrating the EL display shown in FIG. 18 when it is being driven by the analog system. A period from the selection of one gate signal line to the selection of a next different gate signal line is called a one line period (L). In addition, a period from the display of one image to the display of the next image corresponds to a one frame period (F). In the case of the EL display of FIG. 18, there are xe2x80x9cyxe2x80x9d number of the gate signal lines and thus a xe2x80x9cyxe2x80x9d number of line periods (L1 to Ly) are provided in one frame period.
Because the number of line periods in one frame period increases as resolution becomes higher, driver circuits must be driven at high frequencies.
First of all, the power supply lines (V1 to Vx) are held at a constant power supply potential, and the opposing electric potential that is the electric potential of the opposing electrode is also held at a constant electric potential. There is a difference in electric potential between the opposing electric potential and the power supply potential to a degree that the EL element can emit light.
A gate signal from the gate signal line driver circuit is fed to the gate signal line G1 in the first line period (L1). An analog video signal is then sequentially inputted to source signal lines (S1 to Sx). All the switching TFTs connected to the gate signal line G1 are turned ON to thereby feed the analog video signal that is inputted to the source signal lines to the gate electrode of the EL driver TFT through the switching TFT.
The amount of current flowing in a channel forming region of the EL driver TFT is controlled by the level (voltage) of the electric potential of the signal inputted to the gate electrode of the EL driver TFT. Accordingly, the electric potential applied to the pixel electrode of the EL element is determined by the level of the electric potential of the analog video signal that is inputted to the gate electrode of the EL driver TFT. The emission of light by the EL element is thus controlled by the electric potential of the analog video signal.
The above described operation is repeated and the first line period (L1) ends upon the completion of inputting the analog video signal to the source signal lines (S1 to Sx). Next, a gate signal is fed to the gate signal line G2 in the second line period (L2). Similar to the first line period (L1), an analog video signal is sequentially inputted to the source signal lines (S1 to Sx).
When the gate signals have been inputted to all the gate signal lines (G1 to Gy), all the line periods (L1 to Ly) are completed to thereby complete one frame period. Display is performed by all the pixels in the one frame period to form one image.
Thus, the luminous amount emitted by the EL element is controlled by the analog video signal and gray-scale display is therefore performed by this control of the luminous amount of emitted. This system is a driving system which is referred to as the so-called analog drive method where gray-scale display is performed by the variations of the electric potential of the analog video signal fed to the source signal lines.
The state in which the amount of current supplied to the EL element is controlled by the gate voltage of the EL driver TFT will be explained in detail using FIGS. 20A and 20B.
FIG. 20A is a graph showing a current-voltage characteristic of the EL element. When a voltage exceeding a certain threshold value is applied to the EL element, the current through the EL element changes exponentially with respect to a change in the applied voltage.
FIG. 20B is a graph for evaluation of the current through the EL element, in which xcex94V represents the difference between the power supply potential and the opposing potential; VEL, a voltage applied to the EL element (called EL drive voltage); Vds, a voltage applied between the source and the drain of the EL driver TFT (called drain voltage); and Vgs, a voltage applied between the gate and the source of the EL driver TFT (called gate voltage). FIG. 20B shows a curve representing the current-voltage characteristic of the EL element and curves formed in such a manner that curves representing current-voltage characteristics of the EL driver TFT with respect to several gate voltages are flipped about a xcex94V/2 line. The EL driver TFT and the EL element are connected in series, and the current flowing through the EL driver TFT and the EL element can be read from the points of intersection in the graph of FIG. 20B. With respect to any gate voltage, the current flowing through the EL driver TFT and the EL element can also be read in the same manner.
When the switching TFT is turned ON to input an analog video signal to the pixel, the potential of the analog video signal is applied to the gate electrode of the EL driver TFT. At this time, the current flowing through the EL element is determined in the one-to-one relationship with the gate voltage according to the current-voltage characteristic shown in FIG. 20B. That is, the current flowing through the EL element is determined with respect to the voltage of the analog video signal inputted to the gate electrode of the EL driver TFT, and the EL element emits a luminous amount corresponding to the current.
The luminous amount by the EL element is thus controlled by the video signal, and gray-scale display is performed in accordance with this control of the luminous amount.
However, the above-described analog drive has a drawback of being easily influenced by TFT characteristic variation. For example, in a case where the switching TFTs of a plurality of pixels have different current-voltage characteristics and are operated to display the same level of gray-scale, the currents flowing through the switching TFTs vary and different gate voltages, depending on the variations of the currents, are applied to the EL driver TFTs of the pixels. Different currents are thereby caused to flow through the EL elements (see FIG. 20B), so that the EL elements emits different luminous amounts, resulting in failure to uniformly display the gray-scale.
In the case where the current-voltage characteristics of the EL driver TFTs vary, characteristics of the EL driver TFTs shown in FIG. 20 are changed, and different currents flow through the EL element even when the gate voltages applied to the EL driver TFTs are equal to each other. Moreover, because the current through each EL element changes exponentially with respect to a change in the gate voltage (see FIG. 20A), the difference between the currents flowing through some of the EL elements may become considerably large even if the difference between the current-voltage characteristics of the EL driver TFTs is small. Consequently, even in a case where the current-voltage characteristics of the EL driver TFTs vary only slightly, a considerably large difference may be caused between the luminous amounts emitted by the EL elements of the adjacent pixels with respect to a certain input signal level.
In fact, the characteristic variation of the TFT becomes a multiplier effect of both of the variations of the switching TFT and the EL driver TFT, thereby becoming more conditionally severe. Thus, the analog drive is very susceptible to the characteristic variation of the TFT, a point which had become an obstacle in the gray-scale display of conventional active matrix EL displays.
The present invention has been made in view of the above problem, and an object of the present invention is therefore to provide an active matrix EL display device capable of performing clear multiple gray-scale color display. Another object of the present invention is to provide a high-performance electronic equipment (electronic device) incorporating such an active matrix EL display as its display unit.
The inventors of the present invention considered the principle of the analog drive to be inseparable from the system of controlling a gate voltage by an analog video signal and controlling a current through an EL element by the gate voltage.
In the case of the conventional analog drive, since the current flowing through the EL element changes abruptly when the gate voltage changes, the current through the EL element is liable to be influenced by variation in the characteristics of the TFT. In other words, even when the same analog video signal is inputted to a plurality of pixels, the gate voltages applied to an EL driver TFTs vary due to variations in the characteristics of the TFTs. Also, even if the gate voltages applied to the EL driver TFTs are equal, the currents flowing through the EL elements may vary largely, resulting in failure to obtain the desired gray-scale level.
The inventors of the present invention then studied a system for controlling the luminous amount emitted by each EL element through control of the time period during which the EL element emits light, instead of controlling the current through the EL element using an analog video signal. In such a method, a digital signal (called digital data signal) is used as the video signal, and each of the EL driver TFT and the EL element has two states: the ON state and the OFF state, or the luminescing state and the non-luminescing state. According to the present invention, the luminous amount emitted by the EL element is controlled based on such control with respect to time to perform gray-scale display. A drive method in which the time during which the EL element emits light is controlled to perform gray-scale display is called a time-division drive method. Also, gray-scale display performed by the time-division drive method is called time-division gray-scale display.
According to the present invention, by using the above-described system, nonuniformity of the currents outputted from TFTs when the gate voltages applied to the TFTs are equal can be limited even if the characteristics of the TFTs vary to some extent. Thus, it is possible to avoid occurrence of a large difference between the luminous amounts of adjacent pixels due to variations of the characteristics of the TFTs when signals having the same voltage level are inputted to the TFTs.
More specifically, time-division gray-scale display is performed as described below. Display of 2n gray-scale levels using an n-bit digital data signal will be described. An EL display of the present invention described below has pairs of source signal line driver circuits and pairs of gate signal line driver circuits. First, one frame period is divided into an (n) number of display periods (Tr1 to Tm). A time period in which n-bit digital data signals are inputted to all the pixels in the display area to perform display is called a frame period, and regions defined by further dividing one frame period are called display periods (Tr1 to Trn).
In ordinary EL displays, it is preferable to set 60 or more frame periods per second. If the number of images displayed per second is less than 60, there is a possibility of flicker becoming easily visible.
During each of the display periods (Tr1 to Trn), display is performed on the basis of one-bit digital data signal in n-bit digital data signals, which one-bit digital data is inputted in one of an (n) number of writing-in periods (Ta1 to Tan) in one frame period. The writing-in period that comes first is represented by Ta1 and the subsequent writing-in periods are represented by Ta2, Ta3, . . . , Tan in order with respect to time. The corresponding display periods appear in the order of Tr1 to Trn. In each of the writing-in periods (Ta1 to Tan), one of each pair of the source signal line driver circuit and the gate signal line driver circuit.
Each pixel has one EL element. The EL element is formed of an anode, a cathode, and an EL layer interposed between the anode and the cathode. One of the anode and the cathode is called a pixel electrode, and is connected to the source region or the drain region of TFTs. The other of the anode and the cathode is called an opposing electrode, and a predetermined potential (opposing potential) is applied to the opposing electrode through a wiring.
In the present invention, each of the opposing potential and the power supply potential is always maintained at a constant level. The potential difference between the opposing potential and the power supply potential is set to such a value that the EL element produces a sufficient luminous amount when the power supply potential is applied to the pixel electrode. The power supply potential is a potential applied to the pixel electrode when the TFT connected to the pixel electrode of the EL element is in the ON state.
A digital data signal inputted to one pixel in each writing-in period selects the state of the EL element of the pixel (luminescing or non-luminescing). When a bit of the digital data signal for selecting the luminescing state is inputted to the pixel, the power supply potential is immediately applied to the pixel electrode of the EL element of the pixel, thereby causing the EL element of luminesce. On the other hand, when a bit of the digital data signal for selecting the non-luminescing state is inputted to the pixel, the pixel electrode of the EL element of the pixel is immediately disconnected from a wiring for supplying the power supply potential (called a power supply line). so that the EL element does not luminesce. The bit of digital data signal inputted to the pixel is held until the next bit of the digital data signal is inputted. In other words, the EL element of the pixel is maintained in the luminescing or non-luminescing state until the next bit of digital data signal is inputted.
Thus, when one of the writing-in periods (Ta1 to Tan) begins, and when a bit of a digital data signal is inputted, the corresponding display period (one of Tr1 to Trn) begins immediately. When the next writing-in period begins, and when another bit of the digital data signal is inputted, the display period terminates immediately. Simultaneously, the next display period begins. That is, each of the display periods (Tr1 to Trn) is determined by the time difference between the moment at which one of the writing-in periods (Ta1 to Tan) begins and the moment at which the next writing-in period begins.
As bits of the digital data signal are inputted to the pixels in the writing-in periods (Ta1 to Tan), n display periods (Tr1 to Trn) appear successively. The nth bit of the digital data signal is held in the pixel until the first bit of the digital data signal is again inputted. When the first bit of the digital data signal is again inputted, the display period Trn terminates and the frame period also terminates simultaneously.
The lengths of the display periods (Tr1 to Trn) are set so that their lengths arranged in increasing order are in proportions of 20:21:22 . . . 2(nxe2x88x922): . . . :2(nxe2x88x921). Gray-scale display using desired levels in 2n gray-scale levels can be performed by selecting a combination of these display periods.
The gray-scale level of one pixel in display during one frame period is determined as the total sum of the lengths of the display periods during which the corresponding EL element emits light in the frame period. For example, a case is which n=8 and display periods are set so as to appear in increasing order is considered. If the luminance of the pixel when the pixel luminesces through all the display periods is 100%, a 1% luminance can be expressed by luminescence of the pixel through the periods Tr1 and Tr2. Also, a 60% luminance can be expressed by luminescence of the pixel when the periods Tr3, Tr5, and Tr8 are selected.
In the present invention, it is possible to perform display through each pixel even in the writing-in period. Therefore, the proportion of the total sum of the lengths of the display periods in one frame (duty ratio) can be set to a higher value.
In the present invention, a pair of gate signal line driver circuits and a pair of source signal line driver circuits are provided and different gate signal line driver circuits and different source signal line driver circuits may be used with respect to each adjacent pair of the writing-in periods to enable to overlap the two writing-in periods each other. For example, the writing-in period Ta2 can begin before the end of the writing-in period Ta1. Overlapping of the writing-in periods described above enables each display period to be set so as to be shorter than the corresponding writing-in period. Consequently, an extremely short display period can be set to realize a large number of gray-scale levels.
In the present invention, it is necessary that each of the sums Tr1+Tr2, Tr2+Tr3, . . . , Trn+(initial display period Tr1 for the next frame) of the adjacent pairs of the display periods be equal to or greater than the length of the corresponding one of the writing-in periods Ta1, Ta2, . . . , Tan. Needless to say, it is also necessary that the sum of the lengths of the writing-in periods for writing with one gate signal line driver circuit is shorter than one frame period.
The above-described power supply potential and opposing potential are supplied through an IC or the like externally provided on the EL display of the present invention. In a typical EL display at present, when the luminous amount per unit area that pixel luminesces is 200 cd/m2, about several mA/cm2 of current is required for the unit area of the pixel portion. Therefore, if the screen size is increased, it becomes difficult to control by an external switch the level of the electric potential supplied from the power source provided to the above-mentioned IC or the like. In the present invention, the power supply potential and the opposing potential are always held at a constant level, and hence using a switch to control the level of the electric potential from the power source provided to the IC is not necessary, which makes the present invention useful in realizing a panel with a larger screen size.
The resent invention will be described below with respect to the configuration thereof.
An electronic device comprising a pair of source signal line driver circuits, a pair of gate signal line driver circuits, and a pixel portion, characterized in that: the pixel portion includes a plurality of pixels; the plurality of pixels each have an EL element, a pair of EL driver TFTs, a pair of switching TFTs and a pair of eliminating TFTs; the luminescence of the EL element is controlled by the pair of EL driver TFTs; one of the pair of EL driver TFTs is controlled by one of the pair of switching TFTs and one of the pair of eliminating TFTs; the other of the pair of EL driver TFTs is controlled by the other of the pair of switching TFTs and the other of the eliminating TFTs; and gray-scale display is performed by controlling the luminescence time of the plurality of EL elements.
An electronic device comprising a first source signal line driver circuit, a second source signal line driver circuit, a first gate signal line driver circuit, a second gate signal line driver circuit, a pixel portion, a plurality of first source signal lines connected to the first source signal line driver circuit, a plurality of second signal lines connected to the second source signal line driver circuit, a plurality of first gate signal lines connected to the first gate signal line driver circuit, a plurality of second gate signal lines connected to the second gate signal line driver circuit, and a power supply line, characterized in that: the pixel portion includes a plurality of pixels; the plurality of pixels each have a first switching TFT, a second switching TFT, a first eliminating TFT, a second eliminating TFT, a first EL driver TFT, a second EL driver TFT, and an EL element; a gate electrode of the first switching TFT is connected to the first gate signal line; a gate electrode of the second switching TFT is connected to the second gate signal line; one of a source region and a drain region of the first switching TFT is connected to the first source signal lines, and another thereof is connected to a gate electrode of the first EL driver TFT; one of a source region and a drain region of the second switching TFT is connected to the second source signal lines, and another thereof is connected to a gate electrode of the second EL driver TFT; a gate electrode of the first eliminating TFT is connected to the first gate signal line; a gate electrode of the second eliminating TFT is connected to the second gate signal line; one of a source region and a drain region of the first eliminating TFT is connected to the power supply line, and another thereof is connected to the gate electrode of the second EL driver TFT; one of a source region and a drain region of the second eliminating TFT is connected to the power supply line, and another thereof is connected to the gate electrode of the first EL driver TFT; one of a source region and a drain region of the first EL driver TFT is connected to the power supply line, and another thereof is connected to the EL element; and one of a source region and a drain region of the second EL driver TFT is connected to the power supply line, and another thereof is connected to the EL element
The first switching TFT and the first eliminating TFT can be simultaneously turned ON or OFF, and the second switching TFT and the second eliminating TFT can be simultaneously turned ON or OFF.
The first EL driver TFT and the second EL driver TFT each can be the OFF state when the electric potential of the power supply line is applied to the gate electrode of each EL driver TFT.
There is provided an electronic device characterized in that: an (n) number of writing-in periods Ta1, Ta2, . . . , Tan and an (n) number of display periods Tr1, Tr2, . . . , Trn are provided in one frame period; the (n) number of writing-in periods Ta1, Ta2, . . . , Tan appear in the order; the (n) number of display periods Tr1, Tr2, . . . , Trn appear in the order; the time period from the moment at which one of the (n) number of writing-in periods Ta1, Ta2, . . . , Tan begins to the moment at which the writing-in period subsequent to the one of the (n) number of writing-in periods Ta1, Ta2, . . . , Tan begins corresponds to one of the display periods Tr1, Tr2, . . . , Trn; a writing-in period which appears subsequently to the writing-in period Tan is a writing-in period Ta1xe2x80x2 which appears first in the next frame period; a display period which appears subsequently to the display period Trn is a display period Tr1xe2x80x2 which appears first in the next frame period; the (n) number of writing-in periods Ta1, Ta2, . . . , Tan is divided into an (i) number of writing-in periods (i: an integer equal to or larger than 0 and equal to or smaller than n) and an (nxe2x88x921) number of writing-in periods; in each of the (i) number of writing-in periods, digital data signals are inputted from the first source signal line driver circuit to all of the plurality of pixels through the first source signal line; in each of the (nxe2x88x92i) number of writing-in periods, digital data signals are inputted from the second source signal line driver circuit to all of the plurality of pixels through the second source signal line; in each of the (i) number of writing-in periods, the digital data signals inputted from the second source signal line driver circuit before the (i) number of writing-in periods are erased from all of the plurality of pixels; in each of the (nxe2x88x92i) number of writing-in periods, the digital data signals inputted from the first source signal line driver circuit before the (nxe2x88x92i) number of writing-in periods are erased from all of the plurality of pixels; adjacent pairs (Ta1, Ta2), (Ta2, Ta3), . . . , (Ta(nxe2x88x921), Tan), (Tan, Ta1xe2x80x2) between the group of the (n) number of writing-in periods Ta1, Ta2, . . . , Tan and the subsequent group of the (n) number of writing-in periods Ta2, Ta3, . . . , Ta1xe2x80x2 are divided into a group of a (j) number of adjacent pairs of writing-in periods (j: an integer equal to or greater than 0 and equal to or smaller than (nxe2x88x921)) and an (nxe2x88x92j) number of adjacent pairs of writing-in periods; in each of the (j) number of adjacent pairs of writing-in periods, the two writing-in periods overlap each other; in each of the (nxe2x88x92j) number of adjacent pairs of writing-in periods, the two writing-in periods do not overlap each other; in one writing-in period in each of the (j) number of adjacent pairs of writing-in periods, the digital data signals are inputted from the first source signal line driver circuit to all of the plurality of pixels and, in the other writing-in period, the digital data signals are inputted from the second source signal line driver circuit to all of the plurality of pixels;
in each of the (n) number of writing-in periods Ta1, Ta2, . . . , Tan, one of a luminescing state and a non-luminescing state of the EL element of each of the plurality of pixels is selected by the digital data signal inputted to the plurality of pixels; in each of the (n) number of display periods Tr1, Tr2, . . . , Trn, the EL element of each of the plurality of pixels is set in one of the luminescing state and the non-luminescing state according to the digital data signal; in each of an (m) number of display periods (m: an integer equal to or larger than 0 and equal to or smaller than n) in the (n) number of display periods Tr1, Tr2, . . . , Trn, all of the EL elements of the plurality of pixels are set in the non-luminescing state; and the length of each of the sums Tr1+Tr2, Tr2+Tr3, . . . , Trn+Tr1xe2x80x2 of the lengths of adjacent pairs between the group of the (n) number of display periods Tr1, Tr2, . . . , Trn and the subsequent group of the (n) number of display periods Tr2, Tr3, . . . , Tr1xe2x80x2 is equal to or longer than the length of the writing-in periods Ta1, Ta2, . . . , Tan.
The proportions of the lengths of the (nxe2x88x92m) number of display periods may coincide with the proportions of the lengths of an (nxe2x88x92m) number of periods defined by dividing a (k) number of periods T1, T2, . . . , Tk (k: an integer equal to or larger than 1 and equal to or smaller than (nxe2x88x92m)) a (nxe2x88x92mxe2x88x92k) number of times; and if the (k) number of periods T1, T2, . . . , Tk are arranged in increasing order of length, the proportions of the lengths of the (k) number of periods T1, T2. Tk may be expressed by 20:21:2(kxe2x88x921).
The two writing-in periods in at least one of the adjacent pairs of the (n) number of writing-in periods (Ta1, Ta2), (Ta2, Ta3), . . . , (Tan, Ta1xe2x80x2) may overlap each other.
All the EL elements of the plurality of pixels may be set in the non-luminescing state in at least one of the (n) number of display periods Tr1, Tr2, . . . , Trn.
None of the (n) number of display periods Tr1, Tr2, . . . , Trn may be set as a period in which all the EL elements of the plurality of pixels are set in the non-luminescing state.
The lengths of the (i) number of writing-in periods may be equal to each other; and the length of the (nxe2x88x92i) number of writing-in periods may be equal to each other.
All the lengths of the (n) number of writing-in periods Ta1, Ta2, . . . , Tan may be equal to each other.
The (i) number of writing-in periods and the (nxe2x88x92i) number of writing-in periods may appear alternately.
If the (nxe2x88x92m) number of display periods are arranged in increasing order of length, the proportions of the lengths of the (nxe2x88x92m) number of display periods can be expressed by 20:21:2(nxe2x88x92mxe2x88x921).
The source signal line driver circuit is formed on the same substrate as the pixel portion, and the drive frequency may be 10 MHZ or more.
The EL element may have a pixel electrode, an opposing electrode, and an EL layer interposed between the pixel electrode and the opposing electrode.
The opposing electrode may be maintained at a constant potential; and the power supply line may be maintained at a constant potential.
The EL layer may be a low molecular type organic material or a polymer organic material.
The low molecular type organic material may comprise Alq3 (tris-8-quinolilite-aluminum) or TPD (triphenylamine derivative).
The polymer organic material may comprise PPV (polyphenylene vinylene), PVK (polyvinyl carbazole), or polycarbonate.
There is provided an EL display device characterized in that the electronic device is used.
There is provided a video camera characterized in that the electronic device is used.
There is provided a head-mount type EL display device characterized in that the electronic device is used.
There is provided a DVD player characterized in that the electronic device is used.
There is provided a head-mount display characterized in that the electronic device is used.
There is provided a personal computer characterized in that the electronic device is used.
There is provided a portable telephone characterized in that the electronic device is used.
There is provided a car audio characterized in that the electronic device is used.